The five participating research groups share a common interests in understanding the importance and mechanisms of intercellular and hormonal signals that regulate the post-embryonic development and plasticity of neurons. Growing collaboration among these groups over the past 13 years and increasing mutual focus on the mechanisms that control d4evelopmental plasticity within the nervous system have led to the emergence and continued success of this Program Project. Among the research areas represented by these laboratories are: the roles and mechanisms of short-distance and contact-mediate intercellular influences in neural development; hormonally regulated post-embryonic differentiation and remodeling of motor neurons and interneurons; ultrastructural and physiological aspects of synapse formation in developing neural systems; the role of glial cells in the development of organized neuropil in the central nervous system; and molecular mechanisms of steroid hormone regulation of neuronal development. The participants will mount multi-disciplinary, highly collaborative investigations of mechanisms underlying five component projects include: (1) the post-embryonic development of a highly-ordered region of the brain that is involved in associated learning; (2) analysis of glial- neuronal interactions in olfactory receptor neuron sorting and in formation of glomerular compartments during development of olfactory pathways; (3) steroid-hormonal regulation of development of identified motor neurons in vivo and in primary cell culture; (4) molecular and genetic analysis of steroid hormone responsive genes and their roles in CNS development; and (5) influence of male-specific olfactory sensory axons on the development of a specialized olfactory glomerulus and mechanisms of signaling by olfactory axons. All of the proposed studies are based on the use of invertebrate model systems that are economical readily Available, and experimentally favorable. Because they have been extensively studied by many investigators, including the participants in this program project, the insect preparations to be used in the proposed studies are especially well understood and favorable for these experiments. Specifically, Manduca and the cockroach offer excellent access to physiological and hormonal mechanisms, whereas Drosophila offers a powerful array of molecular and genetic approaches. The basic mechanisms of development have been conserved during evolution. We expect, therefore, that information obtained in these projects about neural and muscular development in insects will illuminate related phenomena in other animals including human beings.